Terpolymer compositions

ABSTRACT

Salt-tolerant friction-reducing terpolymer compositions are provided. The compositions can be used in a method of reducing friction resulting from turbulent flow in an aqueous fracturing fluid in a subterranean fracturing process.

TECHNICAL FIELD

The present disclosure relates generally to friction-reducingcompositions and more specifically to friction-reducing terpolymercompositions, methods of making the compositions and methods of usingthe compositions in aqueous liquids such as aqueous liquids pumped intosubterranean oil and gas well formations.

BACKGROUND

After oil and gas wells are drilled, cased, and cemented it is oftennecessary to stimulate the reservoir in order for production fluids toflow economically from the well. The fracturing process involves pumpingaqueous fluids into the well at a rate sufficient to fracture the rock.

From pumping aqueous liquids at rates sufficient to fracture rock,turbulence develops, creating friction pressure, or drag, resulting insubstantial pump energy loss which could otherwise be directed towardsfracturing rock. It is thus typical in the fracturing industry to injectmaterials in small amounts which suppress drag (and thus frictionpressure). This is most commonly accomplished in the oilfield via watersoluble acrylic polymers and copolymers, added in small amounts toaqueous fracturing fluids. The polymers can be delivered during afracturing treatment via several means, though most are delivered viaoil-external emulsion or from dissolving analogous dry polymers.

The surfactants in these friction reducer emulsions are added tostabilize the polymer as a suspension and often possesses low HLB values(generally between 4 and 8). Upon contact with water, the emulsion“inverts”, resulting in polymer transfer to the water. The inversion istypically facilitated through the use of a subsequent water-soluble“inverting surfactant” of HLB greater than 7. The inverting surfactantmay be part of the inverting polymer emulsion, or added to the aqueoussolution in which the emulsion is to be inverted.

One problem with known oil-continuous emulsion treatments is that theinverting surfactants may adversely interact with the emulsion anddestabilize it. Thus usually inverting surfactants are added toemulsions at less than 5%. Polymer emulsions with this low amount ofinverting surfactant may not provide the desired friction reductionbecause the polymer emulsion either does not invert completely or is nottolerant of concentrated brine nor acidic water found in natural oilwell reservoir for example.

SUMMARY

In one aspect, disclosed is a friction reducing terpolymer, comprising acationic monomer, a nonionic monomer, and a monomer having a pendantalcohol moiety.

In another aspect, disclosed is a method of synthesizing a terpolymer asan oil-continuous emulsion, the method comprising: combining analiphatic oil and a surfactant to provide a first mixture; adding acationic monomer, a nonionic monomer, a monomer having a pendant alcoholmoiety, and a salt to the combined aliphatic oil and surfactant toprovide a second mixture; adding a free radical initiator in analiphatic hydrocarbon slurry to the second mixture to provide a reactantmixture; and heating the reactant mixture to provide a terpolymer as anoil-continuous emulsion.

In still another aspect, disclosed is a method of reducing frictionresulting from turbulent flow in an aqueous fracturing fluid in asubterranean fracturing process, the method comprising adding to theaqueous fracturing fluid an effective friction-reducing amount of aterpolymer.

In still another aspect, disclosed is a method of reducing frictionresulting from turbulent flow in an aqueous fracturing fluid in asubterranean fracturing process, the method comprising adding afriction-reducing composition to the aqueous fracturing fluid; whereinthe friction-reducing composition comprises, by weight, about 30% toabout 40% water, about 30% to about 40% a terpolymer, about 20% to about30% an aliphatic oil, and about 2% to about 5% a surfactant.

The advantages of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the aspects describedbelow. The advantages described below will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary laboratory setup for preparing the disclosedcompositions.

FIG. 2 depicts friction reduction performance of an exemplaryembodiment.

DETAILED DESCRIPTION

Disclosed herein are salt-tolerant friction-reducing compositions. Thecompositions can be used to reduce friction resulting from turbulentflow in an aqueous fluid (e.g., an aqueous fracturing fluid in an oilfield fracturing process). Also disclosed are methods of using thesalt-tolerant friction-reducing compositions to reduce friction in anaqueous fluid, the methods including adding to an aqueous fluid aneffective amount of salt-tolerant friction-reducing composition.

The disclosed compositions provide several advantages over knownfriction-reducing compositions. As one advantage, the disclosedcompositions can be used for friction-reduction in an aqueous fluidhaving high salt content (e.g., total dissolved solids of 200,000 mg/Lor greater), without employing a complexing agent, such as ethylenediamine tetra-acetic acid tetrasodium salt and other small-moleculecarboxylates, or phosphates. As another advantage, the disclosedcompositions can be used for friction-reduction in an aqueous fluidwithout including a surfactant in the compositions, or optionally, witha single surfactant, preferably having a hydrophilic-lipophilic balance(HLB) of less than 7. Another advantage is incorporation of novelstabilizing surfactants based on Elevance® 1000 (methyl-9-decenoate) andElevance® 1200 (methyl-9-dodecenoate) metathesis-derived ester alkenes.The Elevance additives help with shelf life stability, and for improvinginversion in field applications.

1. Definition of Terms

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. In case of conflict, the present document, includingdefinitions, will control. Preferred methods and materials are describedbelow, although methods and materials similar or equivalent to thosedescribed herein can be used in practice or testing of the presentinvention. All publications, patent applications, patents and otherreferences mentioned herein are incorporated by reference in theirentirety. The materials, methods, and examples disclosed herein areillustrative only and not intended to be limiting.

The terms “comprise(s),” “include(s),” “having,” “has,” “can,”“contain(s),” and variants thereof, as used herein, are intended to beopen-ended transitional phrases, terms, or words that do not precludethe possibility of additional acts or structures. The singular forms“a,” “an” and “the” include plural references unless the context clearlydictates otherwise. The present disclosure also contemplates otherembodiments “comprising,” “consisting of” and “consisting essentiallyof,” the embodiments or elements presented herein, whether explicitlyset forth or not.

The conjunctive term “or” includes any and all combinations of one ormore listed elements associated by the conjunctive term. For example,the phrase “an apparatus comprising A or B” may refer to an apparatusincluding A where B is not present, an apparatus including B where A isnot present, or an apparatus where both A and B are present. The phrases“at least one of A, B, . . . and N” or “at least one of A, B, . . . N,or combinations thereof” are defined in the broadest sense to mean oneor more elements selected from the group comprising A, B, . . . and N,that is to say, any combination of one or more of the elements A, B, . .. or N including any one element alone or in combination with one ormore of the other elements which may also include, in combination,additional elements not listed.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). The modifier “about” shouldalso be considered as disclosing the range defined by the absolutevalues of the two endpoints. For example, the expression “from about 2to about 4” also discloses the range “from 2 to 4.” The term “about” mayrefer to plus or minus 10% of the indicated number. For example, “about10%” may indicate a range of 9% to 11%, and “about 1” may mean from0.9-1.1. Other meanings of “about” may be apparent from the context,such as rounding off, so, for example “about 1” may also mean from 0.5to 1.4.

The term “gpm” means gallons per minute.

The term “gpt” means gallons per thousand gallons.

The term “gptg” means gallons per thousand gallons.

The term “pptg” means pounds per thousand gallons.

The term “wt. %” means weight percent.

The term “w/w” means weight per weight.

The term “amphoteric” refers to surfactants that have both positive andnegative charges. The net charge of the surfactant can be positive,negative, or neutral, depending on the pH of the solution.

The term “anionic” means a compound that possesses a net negativecharge.

The term “cationic” means a compound that possesses a net positivecharge.

The term “monomer” may refer to a polymerizable allylic, vinylic, oracrylic compound. The monomer may be anionic, cationic, or nonionic.

Exemplary anionic monomers include, but are not limited to,(meth)acrylic acid, and it's salts, including, but not limited toacrylic acid, sodium acrylate, ammonium acrylate, methacrylic acid,sodium methacrylate, and ammonium methacrylate;2-acrylamido-2-methylpropanesulfonic acid (AMPS) and its sodium salt;vinyl sulfonic acid and its salts including sodium vinyl sulfonate;styrene sulfonic acid and its salts; maleic acid and it's salts,including, but not limited to the sodium salt and ammonium salt;sulfopropyl acrylate or methacrylate or other water-soluble forms ofthese or other polymerisable carboxylic or sulphonic acids;sulfomethylated acrylamide; allyl sulfonate; itaconic acid,acrylamidomethylbutanoic acid; fumaric acid; vinylphosphonic acid;allylphosphonic acid, phosphonomethylated acrylamide, and the like.

Exemplary cationic monomers include, but are not limited to,dialkylaminoalkyl acrylates and methacrylates and their quaternary oracid salts, including, but not limited to, dimethylaminoethyl acrylatemethyl chloride quaternary salt, dimethylaminoethyl acrylate methylsulfate quaternary salt, dimethyaminoethyl acrylate benzyl chloridequaternary salt, dimethylaminoethyl acrylate sulfuric acid salt,dimethylaminoethyl acrylate hydrochloric acid salt, diethylaminoethylacrylate, methyl chloride quaternary salt, dimethylaminoethylmethacrylate methyl chloride quaternary salt, dimethylaminoethylmethacrylate methyl sulfate quaternary salt, dimethylaminoethylmethacrylate benzyl chloride quaternary salt, dimethylaminoethylmethacrylate sulfuric acid salt, dimethylaminoethyl methacrylatehydrochloric acid salt, dimethylaminoethyl methacryloyl hydrochloricacid salt, dialkylaminoalkylacrylamides or methacrylamides and theirquaternary or acid salts such as acrylamidopropyltrimethylammoniumchloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt,dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropylacrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammoniumchloride, dimethylaminopropyl methacrylamide methyl sulfate quaternarysalt, dimethylaminopropyl methacrylamide sulfuric acid salt,dimethylaminopropyl methacrylamide hydrochloric acid salt,diethylaminoethylacrylate, diethylaminoethylmethacrylate anddiallyldialkylammonium halides such as diallyldiethylammonium chlorideand diallyldimethyl ammonium chloride.

Exemplary nonionic monomers include, but are not limited to, acrylamide,methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide,N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide,N-vinylmethylacetamide, dim ethylhydroxypropyl (meth)acrylate,hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropylacrylate, hydroxypropyl methacrylate, N-t-butylacrylamide,N-methylolacrylamide, vinyl acetate, acrylonitrile, 2-ethylhexylacrylate, and the like.

The term “fracturing” refers to the process and methods of breaking downa geological formation (e.g., the rock formation around a well bore, bypumping fluid at very high pressures, in order to increase productionrates from a hydrocarbon reservoir).

The term “proppant” refers to a granular substance suspended in thefracturing fluid during the fracturing operation, which serves to keepthe formation from closing back down upon itself once the pressure isreleased. Exemplary proppants include, but are not limited to, 20-40mesh sand, resin-coated sand, sintered bauxite, glass beads, and similarmaterials.

The term “surfactant” refers to a soluble, or partially soluble compoundthat reduces the surface tension of liquids, or reduces interfacialtension between two liquids, or a liquid and a solid by congregating andorienting itself at these interfaces.

For the recitation of numeric ranges herein, each intervening numberthere between with the same degree of precision is explicitlycontemplated. For example, for the range of 6-9, the numbers 7 and 8 arecontemplated in addition to 6 and 9, and for the range 6.0-7.0, thenumber 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 areexplicitly contemplated.

2. Friction Reducing Compositions

Disclosed are salt-tolerant friction reducing compositions. Thecompositions include at least one terpolymer, at least one aliphaticoil, at least one surfactant, and water. The compositions may include asalt. The compositions may include a free radical initiator. Thecompositions may include a chelant. The compositions may be essentiallyfree of a chelant. The compositions may comprise no chelant. Thecompositions may include one or more additional components.

a. Terpolymer

The disclosed compositions include at least one terpolymer component.The terpolymer may be a dispersion polymer or an emulsion polymer. Theterpolymer may be a cationic polymer. The terpolymer may be a syntheticpolymer comprising a variety of monomeric units. In certain embodiments,the terpolymer comprises one or more nonionic monomers, one or morecationic monomers, and one or more monomers having a pendant alcoholmoiety. In certain embodiments, the terpolymer does not include ananionic monomer content.

The terpolymer content of the disclosed compositions may range fromabout 20% to about 50%, about 30% to about 50%, about 20% to about 40%,about 30% to about 40%, about 30% to about 38%, about 32% to about 38%,about 34% to about 38%, about 34% to about 36%, about 35% to about 38%,or about 35% to about 36%, based on total weight of the composition. Theterpolymer content of the disclosed compositions may be about 20%, about25%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%,about 35.5%, about 36%, about 37%, about 38%, about 39%, about 40%,about 45%, or about 50%, based on total weight of the composition. Incertain embodiments, the terpolymer content of the disclosedcompositions is about 35.5%, based on total weight of the composition.

Nonionic Monomer

The terpolymer includes at least one nonionic monomer. The nonionicmonomer may be acrylamide, methacrylamide, N-methylacrylamide,N,N-dimethyl(meth)acrylamide, octyl acrylamide,N(2-hydroxypropyl)methacrylamide, N-methylolacrylamide,N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide,poly(ethylene glycol)(meth)acrylate, poly(ethylene glycol) monomethylether mono(meth)acrylate, N-vinyl-2-pyrrolidone, glycerolmono((meth)acrylate, 2-hydroxyethyl(meth)acrylate, vinyl methylsulfone,or vinyl acetate.

The nonionic monomer content of the terpolymer may be about 30% to about50%, about 35% to about 50%, about 35% to about 45%, about 37% to about45%, about 37% to about 43%, about 39% to about 43%, or about 40% toabout 42%, based on total weight of the terpolymer. The nonionic monomercontent of the terpolymer may be about 30%, about 35%, about 36%, about37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%,about 44%, about 45%, or about 50%, based on total weight of theterpolymer. In certain embodiments, the cationic monomer content of theterpolymer is about 41%, based on total weight of the terpolymer.

ii. Cationic Monomer

The terpolymer includes at least one cationic monomer. The cationicmonomer possesses a positive charge. Representative cationic monomersinclude dialkylaminoalkyl acrylates and methacrylates and theirquaternary or acid salts. The cationic monomer may bedimethylaminoethylacrylate methyl chloride quarternary salt,diallyldimethylammonium chloride (DADMAC),(3-acrylamidopropyl)trimethylammonium chloride (MAPTAC),(3-methacrylamido)propyltrimethylammonium chloride,dimethylaminoethylmethacrylate methyl chloride quarternary salt,dimethylaminoethylacrylate benzylchloride quarternary salt, orN,N-dimethylaminoethyl methacrylate methyl chloride quaternary salt,

The cationic monomer content of the terpolymer may be about 40% to about70%, about 45% to about 70%, about 50% to about 70%, about 50% to about65%, about 55% to about 65%, about 55% to about 60%, about 56% to about60%, or about 57% to about 59%, based on total weight of the terpolymer.The cationic monomer content of the terpolymer may be about 40%, about45%, about 50%, about 55%, about 56%, about 57%, about 58%, about 59%,about 60%, about 61%, about 62%, about 65%, or about 70%, based on totalweight of the terpolymer. In certain embodiments, the cationic monomercontent of the terpolymer is about 58%, based on total weight of theterpolymer.

iii. Monomer Having a Pendant Alcohol

The terpolymer includes at least one monomer having a pendant alcohol.The monomer having a pendant alcohol may provide surface activestability to the terpolymer and provide stability in water, thusproviding surfactancy to the polymer for friction reduction. The monomerhaving a pendant alcohol may stabilize ions that may be present in anaqueous fluid to be treated. In turn, use of a monomer having a pendantalcohol may allow for use of less surfactant in the composition. Themonomer having a pendant alcohol may be N(2-hydroxypropyl)methacrylamide or 2-hydroxyethylmethacrylate. The2-hydroxyethylmethacrylate monomer may also contain a small amount ofhydroxyethyl dimethacrylate or be completely free of the latter monomer.

The monomer having a pendant alcohol content of the terpolymer may beabout 0.1% to about 10%, about 0.1% to about 5%, about 0.5% to about 5%,about 0.5% to about 4%, about 0.5% to about 3%, about 0.5% to about2.5%, about 1.0% to about 2.5%, or about 1.0% to about 2.0%, based ontotal weight of the terpolymer. The monomer having a pendant alcoholcontent of the terpolymer may be about 0.1%, about 0.5%, about 1.0%,about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%,about 1.7%, about 1.8%, about 1.9%, about 2.0%, about 2.5%, about 5%, orabout 10%, based on total weight of the terpolymer. In certainembodiments, the monomer having a pendant alcohol content of theterpolymer is about 1.4%, based on total weight of the terpolymer.

b. Aliphatic Oil

The disclosed compositions may include at least one aliphatic oil. Useof an aliphatic oil promotes formation of an emulsion, allowingproduction of a more active product (more polymer per a given volume ofproduct) compared to dissolution of the polymer in aqueous solution. Thealiphatic oil may be a low viscosity fluid with a kinematic viscosity ofabout 1.0, about 1.1, about 1.2, about 1.3, about 1.4, abut 1.5, about1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2,about 2.3, about 2.4, or about 2.5 centistokes at 40° C. Suitablealiphatic oils include, but not limited to those sold under the Escaid™hydrocarbon fluids trademark by ExxonMobil. For example, the aliphaticoil may be Escaid® Pathfrac and/or a mixture of Pathfrac® HV (highviscosity) grade.

The aliphatic oil content of the disclosed compositions may range fromabout 10% to about 40%, about 15% to about 40%, about 20% to about 40%,about 20% to about 35%, about 20% to about 30%, about 22% to about 28%,about 24% to about 28%, about 25% to about 27%, or about 25% to about26%, based on total weight of the composition. The terpolymer content ofthe disclosed compositions may be about 10%, about 15%, about 20%, about21%, about 22%, about 23%, about 24%, about 25%, about 25.6%, about 26%,about 27%, about 28%, about 29%, about 30%, about 35%, or about 40%,based on total weight of the composition. In certain embodiments, thealiphatic oil content of the disclosed compositions is about 25.6%,based on total weight of the composition.

c. Surfactant

The disclosed compositions may include at least one surfactant. Thesurfactant promotes compatibilization of the aliphatic oil and water toform a stable mixture (emulsion). The surfactant may have ahydrophilic-lipophilic balance (HLB) of less than 7. The surfactant mayhave a HLB of about 1 to about 6, about 1 to about 5, about 2 to about5, about 2 to about 4, about 3 to about 4. The surfactant may have a HLBof about 1, about 2, about 3, about 3.7, about 4, about 5, or about 6.Suitable surfactants include, but are not limited to, ethoxylatedalcohols, ethoxylated castor oils, ethoxylated sorbitan monooleates, andsorbitan sesquioleate and surfactant mixtures of the above withmetathesis-derived alkylate ester surfactants.

The surfactant content of the disclosed compositions may range fromabout 1% to about 10%, about 1% to about 5%, about 2% to about 5%, about3% to about 5%, or about 3% to about 4%, based on total weight of thecomposition. Within these amounts the methathesis-derived alkylateesters can comprise from up to 50% of the total surfactant package andcover the range of C-10 to C-12 alkyl chain lengths of the alkylateester. The surfactant content of the disclosed compositions may be about1%, about 2%, about 3%, about 3.5%, about 4%, about 5%, about 6%, about7%, about 8%, about 9%, or about 10%, based on total weight of thecomposition. In certain embodiments, the surfactant content of thedisclosed compositions is about 3.5%, based on total weight of thecomposition.

d. Water

The disclosed compositions include water. The water content of thedisclosed compositions may range from about 20% to about 50%, about 30%to about 50%, about 20% to about 40%, about 30% to about 40%, about 30%to about 35%, or about 32% to about 33%, based on total weight of thecomposition. The water content of the disclosed compositions may beabout 20%, about 25%, about 30%, about 31%, about 32%, about 32.5%,about 33%, about 34%, about 35%, about 40%, about 45%, or about 50%,based on total weight of the composition. In certain embodiments, thewater content of the disclosed compositions is about 32.5%, based ontotal weight of the composition.

e. Salt

The disclosed compositions may include at least one salt. Suitable saltsinclude, but are not limited to, inorganic salts and organic salts.Exemplary salts include inorganic or organic sulfates, phosphates,chlorides, fluorides, citrates, acetates, tartrates, hydrogen phosphatesor a mixture thereof. Exemplary inorganic salts include ammoniumsulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammoniumhydrogen phosphate, sodium hydrogen phosphate, potassium hydrogenphosphate, sodium chloride and ammonium chloride, or combinationsthereof.

The salt content of the disclosed compositions may range from about 1%to about 10%, about 1% to about 5%, about 1.5% to about 5%, about 1.5%to about 4.5%, about 2% to about 4%, or about 2% to about 3%, based ontotal weight of the composition. The salt content of the disclosedcompositions be about 1%, about 1.5%, about 2%, about 2.5%, about 2.6%,about 2.7%, about 2.8%, about 2.9%, about 3%, about 3.1%, about 3.2%,about 3.3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%,or about 10%, based on total weight of the composition. In certainembodiments, the salt content of the disclosed compositions is about2.8%, based on total weight of the composition.

f. Free Radical Initiator

The disclosed compositions may include at least one oil-soluble freeradical initiator. The polymerization reaction is initiated by anymethod that results in generation of a suitable free radical. Initiationmay be induced through the use of any number of conventional systemsincluding thermal, photochemical, or redox coupled initiation systems.Included are thermally derived radicals, in which the radical speciesresults from thermal, homolytic dissociation of an oil-soluble azo,peroxide, hydroperoxide or perester compound. Exemplary initiatorsinclude 2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis(N,N′dimethyleneisobutylamine) hydrochloride, 2,2′-azobis(2,4-dimethyl valeronitrile) or azobisisobutyronitrile.

The free radical initiator content of the disclosed compositions mayrange from about 0.01% to about 1%, about 0.02% to about 1%, about 0.02%to about 0.1%, or about 0.02% to about 0.05%, based on total weight ofthe composition. The free radical initiator content of the disclosedcompositions may be about 0.01%, about 0.02%, about 0.03%, about 0.04%,about 0.05%, about 0.1%, about 0.5%, or about 1%. In certainembodiments, the free radical initiator content of the disclosedcompositions is about 0.03%, based on total weight of the composition.

g. Chelant

The disclosed compositions may include at least one chelant. The chelantmay ensure a stable product (emulsion) by isolating multivalent ionsduring emulsion preparation. Suitable chelants include, but are notlimited to carbonates, phosphates, pyrophosphates, orthophosphates,citric acid, triethyl citrate, giuconic acid, giucoheptanoic acid,ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) andcombinations thereof. Salts of certain chelating agents may also besuitable. For example, the sodium salt of EDTA, the sodium salt of NTA,and the sodium salt of citric acid may be suitable chelating agents.Examples of suitable phosphates include sodium phosphates. Examples ofsuitable carbonates include sodium carbonate and potassium carbonate.

The chelant content of the disclosed compositions may range from about0.01% to about 1%, about 0.02% to about 1%, about 0.02% to about 0.1%,or about 0.02% to about 0.07%, based on total weight of the composition.The chelant content of the disclosed compositions may be about 0.01%,about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.1%, about0.5%, or about 1%. In certain embodiments, the chelant content of thedisclosed compositions is about 0.05%, based on total weight of thecomposition.

In certain embodiments, the compositions may be essentially free of achelant. In certain embodiments, the compositions may comprise nochelant.

h. Additives

The disclosed compositions may include one or more additional agents.Suitable additives include, but are not limited to corrosion inhibitors,scale inhibitors, friction reducers, biocides, clay swelling inhibitors,hydrogen sulfide scavengers, oxygen scavengers, surfactants, proppants,gravel, fluid loss control additives, emulsion breakers, a plasticizingadditive or any combination thereof. In fracturing embodiments, proppantmay be included in the treatment fluids to prevent the fracture fromcompletely closing when the hydraulic pressure is released.

3. Synthetic Methods

The disclosed compositions may be prepared by synthetic processestypically known by those skilled in the art. In certain embodiments, thealiphatic oil and surfactant are pre-mixed until homogeneous followed byaddition of aqueous components which have also been separately pre-mixedprior to addition to the oil solution. Oxygen is then excluded via inertgas purging or vacuum or both and followed by added heat with stirringto effect radical formation and subsequent polymerization. Typicalpreferred reaction temperature ranges are from 45° C. to about 50° C.over a time necessary for significant conversion followed by additionalheat (60° C. to 65° C. approx.) to more fully convert remaining monomeras well as a final dose of free radical source to substantially completeconversion to polymer. Reaction temperature ranges can be optimized withthermally-activated free radical initiators.

4. Properties of the Compositions

The disclosed compositions can have a combination of desired properties.The compositions can reduce-friction in an aqueous fluid resulting fromturbulent flow in an aqueous fluid. The compositions can also exhibithigh salt tolerance.

a. Friction Reduction

The disclosed compositions provide friction reduction at lowconcentrations (approximately 1.0 gallons per thousand gallons fluid) inhigh-salt brines (e.g., >200,000 ppm salt) under shear (relative tosheared brine water only).

A measured pressure drop of the water traveling at a velocity V througha pipe of length L and diameter d after the addition of the frictionreducing polymer may be compared to the calculated pressure drop for thewater without the friction reducing polymer to determine a % FrictionReduction (“% FR”). In general, a % FR of greater than 50% may beachieved with the addition of an effective amount of the disclosedcompositions to the selected aqueous fluid.

The disclosed compositions can provide for a friction reduction (% FR)in an aqueous fluid (e.g., a fluid having a high salt content) of 50% orgreater, 55% or greater, 60% or greater, 65% or greater, 70% or greater,75% or greater, or 80% or greater, 85% or greater, 90% or greater, or95% or greater. The disclosed compositions can provide for a frictionreduction in an aqueous fluid of about 50%, about 51%, about 52%, about53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%,about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%,about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%,about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%,about 99%, or about 100%.

b. Salt Tolerance

The disclosed compositions can be used for friction reduction in salineconditions (e.g., sea water, brine, or the like). The disclosedcompositions can be used, for example, to reduce friction in sodium,potassium, calcium, magnesium, barium, strontium, chloride, sulfate ionsor any combination thereof. The disclosed compositions can be used forfriction reduction in aqueous fluids having a total dissolved solids of100,000 mg/L or greater, 125,000 mg/L or greater, 150,000 mg/L orgreater, 175,000 mg/L or greater, 200,000 mg/L or greater, 225,000 mg/Lor greater, or 250,000 mg/L or greater.

5. Methods of Use

The disclosed compositions may be used in subterranean treatments wherefriction reduction is desired along with cation solution stability. Suchsubterranean treatments may include, but are not limited to, drillingoperations, stimulation treatments (e.g., fracturing treatments,acidizing treatments, fracture acidizing treatments) and completionoperations. In the fracturing embodiments, the compositions may beintroduced into a subterranean formation at or above a rate sufficientto create or enhance at least one fracture in the subterraneanformation. The disclosed compositions and methods may be especiallyuseful in high-rate water or slick water fracturing treatments.

A method reducing friction in an aqueous fluid can include treating theaqueous fluid with an effective amount of a composition of the presentdisclosure. A method of reducing friction resulting from turbulent flowin an aqueous fracturing fluid in an oil field process can includetreating the aqueous fracturing fluid with an effective amount of acomposition of the present disclosure. The effective amount of thecomposition can vary based on the intended use of the aqueous fluid andthe makeup of the aqueous fluid (e.g., salt content). In certainembodiments, an effective amount of the disclosed composition may be 0.5gallons of composition per thousand gallons of aqueous fluid or less,1.0 gallons of composition per thousand gallons of aqueous fluid orless, 1.5 gallons of composition per thousand gallons of aqueous fluidor less, or 2.0 gallons of composition per thousand gallons of aqueousfluid or less. In certain embodiments, an effective amount of thedisclosed compositions (e.g., 0.5, 1.0, 1.5, or 2.0 gpt) can be used toaccommodate a flow rate of aqueous fluid of 5 gallons per minute orgreater, 10 gallons per minute or greater, 15 gallons per minute orgreater, 20 gallons per minute or greater, 25 gallons per minute orgreater, or 30 gallons per minute or greater.

6. Examples

The foregoing may be better understood by reference to the followingexamples, which are presented for purposes of illustration and are notintended to limit the scope of the invention.

Example 1: Terpolymer Compositions

Exemplary terpolymer compositions can be synthesized as anoil-continuous emulsion wherein one of the three monomers in theterpolymer contains a pendant alcohol moiety. One of the other twomonomers can contain a cationic functionality and the third monomer canbe nonionic. The compositions can include about 35% by weight of theterpolymer in the emulsion, about 4% by weight of a single surfactant,preferably with an HLB of about 3.7, and about 25%-65% by weight of oneor more solvents. Tables 1 and 2 show exemplary terpolymer compositionsprepared according to the present disclosure.

TABLE 1 Terpolymer Composition (1C) Description Raw Material 100 g 1Water Water 32.89 2 Monomer Acrylamide 14.55 3 Monomer[2-(Methacryloyloxy)ethyl]tri- 20.50 methylammonium chloride (DMAEM MeClQuat 75% aqueous) 4 Monomer 2-Hydroxyethylmethacrylate 0.11 5 ChelantEDTA Na₄ 0.05 6 Salt NaCl 2.80 7 Aliphatic oil Escaid ® Pathfrac 25.57 8Soap/Surfactant Span 83 (Sorbitan sesquioleate) 3.50 9 Initiator AIBN(Azo-bis isobutyronitrile) 0.03 Total 100.00

The terpolymer composition of Table 1 can be prepared according to thefollowing steps: (1) aliphatic oil and surfactant (e.g. soap) is addedto a flask (FIG. 1) and stirred until the mixture becomes homogeneous,and the mixture is stirred throughout the remaining steps; (2) thewater, the cationic monomer (e.g., DMAEM MeCI quat), the monomer with apendant alcohol moiety (e.g., 2-hydroxyethylmethacrylate), the nonionicmonomer (e.g., acrylamide), EDTA, and the salt (e.g., NaCl) is added toa separate stirring vessel and is stirred until a homogenous aqueoussolution is formed; (3) the aqueous solution is transferred to the flaskthat contains the aliphatic oil and surfactant; (4) the initiator (e.g.AIBN) is added to the flask via a slurry in the aliphatic oil; (5) thevessel is purged via a nitrogen stream to degas and the flask contentsare heated to 25° C. (or two degrees above ambient temperature), and thecontents are continually stirred approximately 20 minutes with thetemperature monitored (e.g., every 2 minutes); (6) the remainder of theprocedure is switched from nitrogen purge to a nitrogen blanket; (7) thetemperature is increased to approximately 45° C. for approximately 2hours then to approximately 65° C. for approximately one hour; and (8)the heat is turned off, the contents are continually stirred and theproduct is transferred from the vessel at a temperature of about 30° C.or below.

TABLE 2 Terpolymer Compositions (1) (2) (3) Description Raw Material 100g 100 g 100 g 1 Water Water 37.38 37.87 37.27 2 Monomer Acrylamide 14.4314.39 13.91 3 Monomer [2-(Methacryloyloxy)eth- 15.27 15.22 15.90yl]trimethyl ammonium chloride (DMAEM MeCl Quat 75% aqueous) 4 Monomer2-Hydroxyeth- 0.45 0.05 0.45 ylmethacrylate 5 Monomer Ethylene glycol0.01 0.01 0.01 dimethacrylate 6 Monomer Diethylene glycol 0.05 0.05 0.05methacrylate 7 Chelant EDTA Na₄ 0.05 0.05 0.05 8 Salt NaCl 2.80 2.802.80 9 Aliphatic Oil Isoparaffin 25.57 25.57 25.57 10 Soap/ Span 83(Sorbitan 3.5 3.5 3.5 Surfactant sesquioleate) 11 Initiator AIBN(Azo-bis 0.03 0.03 0.03 isobutyronitrile) 12 Monomer 30% sodiumbisulfite 0.01 0.01 0.01 Reactant 13 Surfactant Methyl-9-decenoate 0.450.45 0.45 (Elevance 1000) Total 100 100 100

The terpolymer compositions of Table 2 can be prepared according to thefollowing steps: (1) aliphatic oil and surfactant (e.g. soap) is addedto a flask (FIG. 1) and stirred until the mixture becomes homogeneous,and the mixture is stirred throughout the remaining steps; (2) thewater, the cationic monomer (e.g., DMAEM MeCI quat), the monomer with apendant alcohol moiety (e.g., 2-hydroxyethylmethacrylate), the nonionicmonomer (e.g., acrylamide), the monomer Ethylene glycol dimethacrylate,the monomer Diethylene glycol methacrylate, EDTA, and the salt (e.g.,NaCl)) is added to a separate stirring vessel and is stirred until ahomogenous aqueous solution is formed; (3) the aqueous solution istransferred to the flask that contains the aliphatic oil and surfactant;(4) the initiator (e.g. AIBN) is added to the flask via a slurry in thealiphatic oil; (5) the vessel is purged via a nitrogen stream to degasand the flask contents are heated to 25° C. (or two degrees aboveambient temperature), and the contents are continually stirredapproximately 20 minutes with the temperature monitored (e.g., every 2minutes); (6) the remainder of the procedure is switched from nitrogenpurge to a nitrogen blanket; (7) the temperature is increased toapproximately 45° C. for approximately 2 hours then to approximately 65°C. for approximately 1 hour; and (8) the heat is turn off, the contentsare continually stirred until the vessel is cooled to a temperature ofbetween 35° C. and 40° C.; (9) the temperature is maintained at 35° C.and 40° C. and 30% sodium bisulfite is added and stirred for 30 minutes;(10) Elevance is added and is continually stirred over 15 minutes andthe product is transferred from the vessel at a temperature of about 30°C. or below.

Example 2. Friction Reduction Performance

Compositions of the present disclosure were evaluated for frictionreduction performance in different water systems having a high saltcontent.

Equipment and Procedures: The measurement system includes a 57 foot loopof one-half inch 316 stainless steel tubing (inner diameter=0.43 inch),a Moyno-type pump, a mixing/addition vessel, a liquid flow meter, andtwo pressure transducers. The system is filled with 9 gallons of theBase Water and a flow rate of 10 gallons per minute (gpm) is establishedand maintained. The baseline differential pressure (dP) is measuredversus the flow rate. At two minutes elapsed time, the friction reducingcomposition is injected. The rate is maintained at 10 gpm for 15minutes; the rate is increased to 15 gpm for 10 minutes; the rate isincreased to 20 gpm for 5 minutes; and the rate is decreased to 10 gpmfor 5 minutes before clean up.

Table 3 shows the water mediums tested. Table 4 shows the compositionfrom Table 1 evaluated in the friction reduction experiment. Table 5shows the compositions from Table 2 evaluated in the friction reductionexperiment.

TABLE 3 Base Water Barium Rich Water Sodium 56,100 mg/L Potassium 2,550mg/L Calcium 18,500 mg/L Magnesium 1,720 mg/L Barium 182 mg/L Strontium1,900 mg/L Chloride 140,300 mg/L Total Dissolved Solids (TDS) 221,300mg/L

TABLE 4 Friction Reduction Results (Sample 1C from Table 1) FR at FR atFR at FR at FR at end of start end FR back Conc. Initial end of start of15 of 20 of 20 at FR Name gpt Fric Red 10 gpm 15 gpm gpm gpm gpm 10 gpmTest Lot gpt % % % % % % % 1 1C 1.5 64 65 68 66 69 67 54

The results of Table 4 is depicted in FIG. 2. In FIG. 2, the “FrictionReduction” line measures percent friction reduction observed as afunction of the pressure drop difference measured at the pipe wallbetween salty water and the friction-reducer-containing salty watersolution. The water gets slicker, and flows more easily due to thepresence of the friction reducer. How well the friction reducer performsrelative to flowing salty water alone determines the overall frictionreducer quality.

Salty water is flowed through the pipe loop for 2 minutes at a pump rateof 10 gallons per minute (gpm), followed by injection of the frictionreducer at a dosage of 1.5 gallons friction reducer per 1,000 gallons(gpt). Upon adding the friction reducer, the “Friction Reduction” lineturns nearly vertical followed by a perpendicular plateau region, andall of which occurs within about a 30 seconds timeframe. This 30 secondsor so timeframe is described as the “quick friction reducer hydrationrate”, or in other words, the friction reducer is dissolving quickly inthe water and is stable, and depicts minimal friction reducer sheardegradation from 2.3 minutes through about 17 cumulative minutes.

Next, the pump rate is increased to 15 gpm and continued for the next 10minutes, and done for the purpose of determining general frictionreducer shear rate stability. Subsequently, the rate is furtherincreased to 20 gpm for about 7 minutes with similar horizontal plateau.Finally, the rate is dropped back to 10 gpm to show friction reductionreversible shear stability.

The “Temperature” line depicts observed flow loop fluid temperature withtime and which indicates a slow heat buildup from shear, beginning atabout 85° F. and increasing to about 97° F. This is considered normalfriction heat buildup.

The “dP Pipe” line depicts the measured relative pressure differencebetween flowing salty water and friction-reducer-containing salty water.The “Rate (gpm)” line indicates the flow rate over time collected from apipe flow meter.

TABLE 5 Friction Reduction results (Samples 1-3 Table 2) FR at FR at FRat Initial FR at FR at end start end FR Conc. Frict end of start of of15 of 20 of 20 back at gpt Red 10 gpm 15 gpm gpm gpm gpm 10 gpm Samplegpt % % % % % % % 1 1.5 65 65 68 69 71 70 60 2 1.5 66 65 68 68 71 71 623 1.5 67 66 69 69 71 70 61

7. Exemplary Embodiments

For reasons of completeness, various aspects of the disclosure are setout in the following numbered clauses:

Clause 1. A friction reducing terpolymer, comprising a cationic monomer,a nonionic monomer, and a monomer having a pendant alcohol moiety.

Clause 2. The terpolymer of clause 1, comprising, by weight, about 50 wt% to about 65 wt % the cationic monomer, about 35 wt % to about 45 wt %the nonionic monomer, and about 0.1 wt % to about 5 wt % of the monomerhaving a pendant alcohol moiety.

Clause 3. The terpolymer of clause 1 or clause 2, wherein the cationicmonomer is N,N-dimethylaminoethyl methacrylate methyl chloridequaternary salt.

Clause 4. The terpolymer of any one of clauses 1-3, wherein the nonionicmonomer is acrylamide.

Clause 5. The terpolymer of any one of clauses 1-4, wherein the monomerhaving a pendant alcohol moiety is 2-hydroxyethylmethacrylate.

Clause 6. The terpolymer of any one of clauses 1-4, wherein the monomerhaving a pendant alcohol moiety is 2-hydroxyethylmethacrylate with orwithout the presence of its dimethyacrylic analogue.

Clause 7. The terpolymer of any one of clauses 1-6, comprising, byweight, 56 wt % to 60 wt % N,N-dimethylaminoethyl methacrylate methylchloride quaternary salt, 39 wt % to 43 wt % acrylamide, and 0.5 wt % to2.5 wt % 2-hydroxyethylmethacrylate.

Clause 8. The terpolymer of any one of clauses 1-7, wherein theterpolymer is an oil-continuous emulsion.

Clause 9. A friction reducing composition, comprising, by weight, about30 wt % to about 40 wt % of a terpolymer according to any one of clauses1-7; about 30 wt % to about 40 wt % water; about 20 wt % to about 30 wt% of an aliphatic oil; and about 2 wt % to about 5 wt % of a surfactant.

Clause 10. The composition of clause 9, further comprising, by weight,about 1.5 wt % to about 4.5 wt % of a salt; about 0.01 wt % to about 0.1wt % of a chelant; and about 0.01 wt % to about 0.1 wt % of a freeradical initiator.

Clause 11. The composition of clause 10, wherein the salt is sodiumchloride, the chelant is ethylene diamine tetraacetic acid tetrasodium(EDTA Na₄), and the free radical initiator is azobisisobutyronitrile.

Clause 12. The composition of clause 10, wherein the salt is sodiumchloride, the chelant is ethylene diamine tetraacetic acid tetrasodium(EDTA Na₄), and the free radical initiator is another oil-soluble azoinitiator.

Clause 13. The composition of any one of clauses 9-12, wherein thesurfactant has a hydrophilic-lipophilic balance value of about 2 toabout 5.

Clause 14. The composition of any one of clauses 9-12, wherein thesurfactant has a hydrophilic-lipophilic balance value of about 3 toabout 4.

Clause 15. The composition of any one of clauses 9-12, wherein thesurfactant has a hydrophilic-lipophilic balance value of about 3.7.

Clause 16. The composition of any one of clauses 9-15, wherein thesurfactant is sorbitan sesquioleate.

Clause 17. The composition of any one of clauses 9-16, wherein thealiphatic oil is a low viscosity fluid with a kinematic viscosity ofabout 1.7 centistokes at 40° C.

Clause 18. The composition of any one of clauses 9-17, comprising, byweight, about 32.5 wt % water, about 35.5 wt % the terpolymer, about25.6 wt % the aliphatic oil, and about 3.5 wt % of surfactant.

Clause 19. The composition of any one of clauses 9-18, comprising, byweight, about 2.8% sodium chloride, about 0.05% ethylene diaminetetraacetic acid tetrasodium (EDTA Na₄), and about 0.03%azobisisobutyronitrile.

Clause 20. A method of synthesizing a terpolymer as an oil-continuousemulsion, the method comprising: combining an aliphatic oil and asurfactant to provide a first mixture; adding a cationic monomer, anonionic monomer, a monomer having a pendant alcohol moiety, and a saltto the combined aliphatic oil and surfactant to provide a secondmixture; adding a free radical initiator in an aliphatic hydrocarbonslurry to the second mixture to provide a reactant mixture; and heatingthe reactant mixture to provide a terpolymer as an oil-continuousemulsion.

Clause 21. The method of claim 20, wherein the terpolymer is theterpolymer of any one of clauses 1-8.

Clause 22. A method of reducing friction resulting from turbulent flowin an aqueous fracturing fluid in a subterranean fracturing process, themethod comprising adding to the aqueous fracturing fluid an effectivefriction-reducing amount of a terpolymer.

Clause 23. The method of clause 22, wherein the terpolymer is theterpolymer of any one of clauses 1-8.

Clause 24. A method of reducing friction resulting from turbulent flowin an aqueous fracturing fluid in a subterranean fracturing process, themethod comprising adding a friction-reducing composition to the aqueousfracturing fluid; wherein the friction-reducing composition comprises,by weight, about 30% to about 40% water, about 30% to about 40% aterpolymer, about 20% to about 30% an aliphatic oil, and about 2% toabout 5% a surfactant.

Clause 25. The method of clause 24, wherein the friction-reducingcomposition is the friction-reducing composition of any one of clauses9-19.

Clause 26. The method of any one of clauses 20-25, wherein thesubterranean fracturing process is achieved in an oil field.

Clause 27. The method of any one of clauses 20-26, wherein the aqueousfracturing fluid has a high salt content.

Clause 28. The method of any one of clauses 20-27, wherein the aqueousfracturing fluid is barium rich water, sulfate rich water, or acombination thereof.

It is understood that the foregoing detailed description andaccompanying examples are merely illustrative and are not to be taken aslimitations upon the scope of the invention, which is defined solely bythe appended claims and their equivalents.

Various changes and modifications to the disclosed embodiments will beapparent to those skilled in the art. Such changes and modifications,including without limitation those relating to the chemical structures,substituents, derivatives, intermediates, syntheses, compositions,formulations, or methods of use of the invention, may be made withoutdeparting from the spirit and scope thereof.

1.-29. (canceled)
 30. A method of synthesizing a terpolymer as anoil-continuous emulsion, the method comprising: combining an aliphaticoil and a surfactant to provide a first mixture; adding a cationicmonomer, a nonionic monomer, a monomer having a pendant alcohol moiety,and a salt to the combined aliphatic oil and surfactant to provide asecond mixture; adding a free radical initiator in an aliphatichydrocarbon slurry to the second mixture to provide a reactant mixture;and heating the reactant mixture to provide a terpolymer as anoil-continuous emulsion.
 31. The method of claim 30, wherein theterpolymer is a friction reducing terpolymer, comprising a cationicmonomer, a nonionic monomer, and a monomer having a pendant alcoholmoiety
 32. A method of reducing friction resulting from turbulent flowin an aqueous fracturing fluid in a subterranean fracturing process, themethod comprising adding to the aqueous fracturing fluid an effectivefriction-reducing amount of a terpolymer.
 33. The method of claim 32,wherein the terpolymer is a friction reducing terpolymer, comprising acationic monomer, a nonionic monomer, and a monomer having a pendantalcohol moiety
 34. A method of reducing friction resulting fromturbulent flow in an aqueous fracturing fluid in a subterraneanfracturing process, the method comprising adding a friction-reducingcomposition to the aqueous fracturing fluid; wherein thefriction-reducing composition comprises, by weight, about 30% to about40% water, about 30% to about 40% a terpolymer, about 20% to about 30%an aliphatic oil, and about 2% to about 5% a surfactant.
 35. The methodof claim 34, wherein the friction-reducing composition comprises byweight, about 30 wt % to about 40 wt % of a terpolymer; wherein theterpolymer is a friction reducing terpolymer, comprising a cationicmonomer, a nonionic monomer, and a monomer having a pendant alcoholmoiety; about 30 wt % to about 40 wt % water; about 20 wt % to about 30wt % of an aliphatic oil; and about 2 wt % to about 5 wt % of asurfactant.
 36. The method of claim 34, wherein the friction-reducingcomposition comprises, by weight, about 30 wt % to about 40 wt % of aterpolymer; wherein the terpolymer is a friction reducing terpolymer,comprising a cationic monomer, a nonionic monomer, and a monomer havinga pendant alcohol moiety; about 30 wt % to about 40 wt % water; about 20wt % to about 30 wt % of an aliphatic oil; and about 2 wt % to about 5wt % of surfactant mixtures (e.g., span 83 and Elevance 1000 or Elevance1200).
 37. The method of claim 32, wherein the subterranean fracturingprocess is achieved in an oil field.
 38. The method of claim 32, whereinthe aqueous fracturing fluid has a high salt content.
 39. The method ofclaim 32, wherein the aqueous fracturing fluid is barium rich water,sulfate rich water, or a combination thereof.